The present invention generally relates to papermaking belts useful in papermaking machines for making strong, soft, absorbent paper products. More particularly, the invention relates to papermaking belts comprising a resinous framework and a reinforcing element joined thereto.
Generally, a papermaking process includes several steps. Typically, an aqueous slurry of papermaking fibers is formed into an embryonic web on a foraminous member, such, for example, as a Fourdrinier wire. After the initial forming of the paper web on the Fourdrinier wire, or forming wires, the paper web is carried through a drying process or processes on another piece of papermaking clothing in the form of endless belt which is often different from the Fourdrinier wire or forming wires. This other clothing is commonly referred to as a drying fabric or belt. While the web is on the drying belt, the drying or dewatering process can involve vacuum dewatering, drying by blowing heated air through the web, a mechanical processing, or a combination thereof.
In through-air-drying processes developed and commercialized by the present assignee, the drying fabric may comprise a so-called deflection member having a macroscopically monoplanar, continuous, and preferably patterned and non-random network surface which defines a plurality of discrete, isolated from one another deflection conduits. Alternatively, the deflection member may comprise a plurality of discrete protuberances isolated from one another by a substantially continuous deflection conduit, or be semi-continuous. The embryonic web is associated with the deflection member. During the papermaking process, the papermaking fibers in the web are deflected into the deflection conduits and water is removed from the web through the deflection conduits. The web then is dried and can be foreshortened, by, for example, creping. Deflection of the fibers into the deflection conduits of the papermaking belt can be induced by, for example, the application of differential fluid pressure to the embryonic paper web. One preferred method of applying differential pressure is exposing the web to a fluid pressure differential through the drying fabric comprising the deflection member.
Through-air-dried paper webs may be made according to any commonly assigned and incorporated herein by reference U.S. Pat. No. 4,529,480 issued to Trokhan on Jul. 16, 1985; U.S. Pat. No. 4,637,859 issued to Trokhan on Jan. 20, 1987; U.S. Pat. No. 5,364,504, issued to Smurkoski et al. on Nov. 15, 1994; U.S. Pat. No. 5,259,664, issued to Trokhan et al. on Jun. 25, 1996; and U.S. Pat. No. 5,679,222, issued to Rasch et al. on Oct. 21, 1997.
Generally, a method of making the deflection member comprises applying a coating of liquid photosensitive resin to a surface of a foraminous element, controlling the thickness of the coating to a pre-selected value, exposing the coating of the liquid photosensitive resin to light in an activating wave-length through a mask, thereby preventing or reducing curing of selected portions of the photosensitive resin. Then the uncured portions of the photosensitive resin are typically washed away by showers. Several commonly assigned U.S. patents which are incorporated herein by reference, disclose papermaking belts and methods of making the belts: U.S. Pat. No. 4,514,345, issued Apr. 30, 1985 to Johnson et al.; U.S. Pat. No. 4,528,239, issued Jul. 9, 1985 to Trokhan; U.S. Pat. No. 5,098,522, issued Mar. 24, 1992; U.S. Pat. No. 5,260,171, issued Nov. 9, 1993 to Smurkoski et al.; U.S. Pat. No. 5,275,700, issued Jan. 4, 1994 to Trokhan; U.S. Pat. No. 5,328,565, issued Jul. 12, 1994 to Rasch et al.; U.S. Pat. No. 5,334,289, issued Aug. 2, 1994 to Trokhan et al.; U.S. Pat. No. 5,431,786, issued Jul. 11, 1995 to Rasch et al.; U.S. Pat. No. 5,496,624, issued Mar. 5, 1996 to Stelljes, Jr. et al.; U.S. Pat. No. 5,500,277, issued Mar. 19, 1996 to Trokhan et al.; U.S. Pat. No. 5,514,523, issued May 7, 1996 to Trokhan et al.; U.S. Pat. No. 5,554,467, issued Sep. 10, 1996, to Trokhan et al.; U.S. Pat. No. 5,566,724, issued Oct. 25, 1996 to Trokhan et al.; U.S. Pat. No. 5,624,790, issued Apr. 29, 1997 to Trokhan et al.; U.S. Pat. No. 5,628,876 issued May 13, 1997 to Ayers et al.; U.S. Pat. No. 5,679,222 issued Oct. 21, 1997 to Rasch et al.; and U.S. Pat. No. 5,714,041 issued Feb. 3, 1998 to Ayers et al., the disclosures of which are incorporated herein by reference.
A search for improved methods and products has continued. Now, it is believed that the deflection member may be made by at least several other methods. The present invention provides a novel process and an apparatus for making a papermaking belt by extruding a fluid resinous material onto the reinforcing element according to a desired predetermined pattern and then solidifying the patterned resinous material. The present invention also provides a process and an apparatus that significantly reduce the amount of the resinous material required to construct the papermaking belt comprising a reinforcing element and a patterned resinous framework.
These and other objects of the present invention will be more readily apparent when considered in reference to the following description, in conjunction with the accompanying drawings.
A papermaking belt that can be made by a process and an apparatus of the present invention comprises a reinforcing element and a patterned resinous framework joined thereto. The reinforcing element has a first side and an opposite second side. Preferably, but not necessarily, the reinforcing element comprises a fluid-permeable element, such as, for example, a woven fabric or a screen having a plurality of open areas therethrough. The reinforcing element may also comprise a felt, as for example disclosed in commonly assigned U.S. Pat. Nos. 5,629,052 and 5,674,663, incorporated herein by reference. The resinous framework has a top side and a bottom side, the top and bottom sides corresponding to the first and second sides of the reinforcing element, respectively. The resinous framework may have a substantially continuous pattern, a discrete pattern, or a semi-continuous pattern.
A process for making a papermaking belt includes the following steps: providing a reinforcing element; providing an extrudable resinous material; providing at least a first extrusion die; supplying the resinous material into the extrusion die and extruding the resinous material onto the reinforcing element such that the resinous material and the reinforcing element join together, preferably the resinous material forming a pre-selected pattern on the reinforcing element; and solidifying the resinous material joined to the reinforcing element. Alternatively to extruding the resinous material directly onto the reinforcing element, the resinous material can be extruded onto a forming surface, and then be transferred to the reinforcing element.
In its preferred embodiment, the process is continuous and includes a step of continuously moving the reinforcing element or the forming surface in a machine direction at a transport velocity, and a step of continuously moving of the at least first extrusion die relative to the reinforcing element or the forming surface. Preferably, a plurality of extrusion dies is provided, each die being designed to move relative to the reinforcing element according to a pre-determined pattern. Preferably, each of the extrusion dies is structured to extrude a plurality of beads of the resinous material onto a reinforcing element. The resinous beads extruded onto the reinforcing element may have general orientation in the machine direction, or in the direction substantially orthogonal to the machine direction including any direction which forms an acute angle with the machine direction. In the latter instance, the combined movement of the reinforcing element (or the forming surface) and the extrusion die or dies preferably produces a resulting velocity vector having a machine-directional component and a cross-machine-directional component. The movement of the reinforcing element (or the forming surface) and the movement of the extrusion dies is designed to mutually cooperate such that the resinous material extruded upon the reinforcing element forms a pre-selected, preferably repeating, pattern. The beads may have a waving configuration, or be straight. Also, the beads may have differential height.
The extrusion dies may be designed to move in a direction substantially orthogonal to the machine direction. In one embodiment of the preferred continuous process, at least two extrusion dies move reciprocally in the direction orthogonal to the machine direction. Depending on a specific pre-selected pattern of the resinous framework, the extrusion die or dies may span substantially the entire width of the reinforcing element, orxe2x80x94alternativelyxe2x80x94any portion of the width.
In some embodiments, the extrusion die or dies may have a complex movement, for example, a first reciprocal movement in the direction orthogonal to the machine direction and a second reciprocal movement in the machine direction. An amplitude of the first reciprocal movement is preferably greater than the amplitude of the second reciprocal movement. Then, the resulting pattern of the resinous material extruded onto the reinforcing element comprises a plurality of resinous beads having a waving, or sinusoidal (or oscillating) configuration.
In the most preferred embodiment, the forming surface (or the reinforcing element) is continuously traveling in the machine direction, while the extrusion dies reciprocally move in the cross-machine direction.
In one embodiment, a first plurality of the beads and a second plurality of the beads are extruded onto the forming surface or the reinforcing element in such manner that the first and second pluralities of the beads interconnect when disposed on the forming surface or the reinforcing element, thereby forming the substantially continuous resinous framework. The beads may cross-over, thereby forming xe2x80x9csuper-knucklesxe2x80x9d extending outwardly from the reinforcing element. The super-knuckles, then, can be forced, under pressure, into the reinforcing element such that the reinforcing element and the super-knuckles join together. The rest of the resinous framework may remain not attached to the reinforcing element, thus beneficially providing the belt having a sufficient xe2x80x9cskewabilityxe2x80x9d of the reinforcing element relative to the resinous framework. In such embodiment, the resinous framework is securely joined to the reinforcing element while is also partially movable relative to the reinforcing structure.
The present invention contemplates the use of at least two different resinous material, chemically active relative one another. Then, when the first plurality of resinous beads comprising a first resinous material and a second plurality of resinous beads comprising a second resinous material interconnect (by crossing-over or otherwise) in points of contact when disposed on the reinforcing element or the forming surface, the first resinous material and the second resinous material mutually cross-link at the points of contact.
The step of solidifying the resinous framework joined to the reinforcing structure can be performed by any means known in the art, depending on the nature of the resinous framework. For example, the resinous framework comprising a photosensitive resin can be cured with UV radiation, while thermosetting resins are typically cured by temperature.
The process of the present invention may further include a step of controlling a thickness of the resinous framework to at least one pre-selected value. This could be done by calendering the reinforcing element in combination with the resinous framework, sanding at least one side of the composite, cutting the reinforcing structure with a knife or laser beam, or by any other means known in the art.
The present invention also discloses an apparatus for making the belt, the apparatus comprising a forming surface, a means for moving the forming surface in the machine direction, at least one extrusion die structured to move relative to the forming surface, as discussed above, and a means for causing the resinous framework and the reinforcing element to join together. The apparatus can also comprise a means of controlling the thickness of the resinous framework.
One embodiment of the belt of the present invention comprises at least a first plurality of resinous beads having a first thickness, and a second plurality of resinous beads having a second thickness, wherein the first and second pluralities of the resinous beads at least partially overlap at points of contact thereby forming super-knuckles therein, the super-knuckles having a third thickness greater than either one of the first thickness and the second thickness. The first thickness may be different from the second thickness if so desired. The deflection conduits are disposed intermediate the points of contact. Preferably, the super-knuckles are distributed throughout the reinforcing element in a pre-selected pattern, and more preferably, the patterned resinous framework has a substantially continuous pattern. Alternatively, the patterned resinous framework may have a semi-continuous pattern, or a pattern also comprising a third plurality of discrete protuberances outwardly extending from the reinforcing element.
Preferably, the resinous beads comprise a material selected from the group consisting of epoxies, silicones, urethanes, polystyrenes, polyolefins, polysulfides, nylons, butadienes, photopolymers, and any combination thereof.